1. Field of the Invention
The present invention relates in general to thermal ink jet (TIJ) printheads and more specifically to a system and method for high-performance printing that uses a compact monochrome printhead having staggered, high-density arrangement of ink drop generators.
2. Related Art
Thermal ink jet (TIJ) printers are popular and widely used in the computer field. These printers are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInk Jet Devices,xe2x80x9d Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Ink jet printers produce high-quality print, are compact and portable, and print quickly and quietly because only ink strikes a print medium (such as paper).
An ink jet printer produces a printed image by printing a pattern of individual dots (or pixels) at specific defined locations of an array. These dot locations, which are conveniently visualized as being small dots in a rectilinear array, are defined by the pattern being printed. The printing operation, therefore, can be pictured as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting a small volume of ink onto the print medium. An ink supply device, such as an ink reservoir, supplies ink to the ink drop generators. The ink drop generators are controlled by a microprocessor or other controller and eject ink drops at appropriate times upon command by the microprocessor. The timing of ink drop ejections generally corresponds to the pixel pattern of the image being printed.
In general, the ink drop generators eject ink drops through an orifice (such as a nozzle) by rapidly heating a small volume of ink located within a vaporization or firing chamber. The vaporization of the ink drops typically is accomplished using an electric heater, such as a small thin-film (or firing) resistor. Ejection of an ink drop is achieved by passing an electric current through a selected firing resistor to superheat a thin layer of ink located within a selected firing chamber. This superheating causes an explosive vaporization of the thin layer of ink and an ink drop ejection through an associated nozzle of the printhead.
Ink drop ejections are positioned on the print medium by a moving carriage assembly that supports a printhead assembly containing the ink drop generators. The carriage assembly traverses over the print medium surface and positions the printhead assembly depending on the pattern being printed. The carriage assembly imparts relative motion between the printhead assembly and the print medium along a xe2x80x9cscan axisxe2x80x9d. In general, the scan axis is in a direction parallel to the width of the print medium and a single xe2x80x9cscanxe2x80x9d of the carriage assembly means that the carriage assembly displaces the printhead assembly once across approximately the width of the print medium. Between scans, the print medium is typically advanced relative to the printhead along a xe2x80x9cmedia (or paper) advance axisxe2x80x9d that is perpendicular to the scan axis (and generally along the length of the print medium).
As the printhead assembly is moved along the scan axis a swath of intermittent lines is generated. The superposition of these intermittent lines creates the appearance as text or image of a printed image. Print resolution along the media advance axis is often referred to as a density of these intermittent lines along the media advance axis. Thus, the higher the density of the intermittent lines in the media advance axis the greater the print resolution along that axis.
The density of the intermittent lines along the media advance axis (and thus the print resolution) can be increased by increasing the number of ink drop generators on the printhead. This results in better print resolution and increased print speed. Moreover, due to several factors, it is desirable to increase the number of ink drop generators without increasing the size of the printhead. However, merely increasing the number of drop generators on an existing printhead greatly increases the amount of heat dissipated in the printhead during print operations. This increased heat dissipation can cause unwanted printhead thermal excursions. These large thermal excursions on the printhead adversely affect printhead operation and can cause print quality defects, printhead thermal shutdown and even failure of the entire printhead.
One technique that may be used to avoid large thermal excursions is to slow down the speed of the printhead. This technique, however, negates the positive effect of providing more ink drop generators on the printhead. Another technique that may be used to avoid a large thermal excursion is to increase the size of the printhead. A primary disadvantage of this technique, however, is that increasing printhead size increases the cost of the printing system. This is unacceptable because printing systems are rapidly decreasing in price and a printing system having the added cost of a larger printhead will not be competitive in the marketplace. What is needed, therefore, is a way of providing a compact, high nozzle count, and high performance printhead that does not suffer from deleterious thermal excursions.
To overcome the limitations in the prior art as described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a compact monochrome ink jet printhead having a high-density of ink drop generators. The present invention provides a high-performance design that enable high-resolution and high-speed printing while reducing cost due to an efficient use of printhead space. In particular, the compact, high-performance printhead of the present invention includes several performance improving aspects that allow a large number of ink drop generators to be placed on a compact printhead while minimizing problems such as thermal excursions.
The compact, monochrome ink jet printhead of the present invention enables high-performance printing that includes high-resolution and high-speed printing. In particular, one technique used to increase print resolution and speed is to increase the number of ink drop generators, stagger them with respect to groups of other ink drop generators and operate the ink drop generators at a high frequency. This staggered, high-density arrangement helps increase an effective resolution of the printhead. The present invention includes a high-density staggered arrangement of ink drop generators disposed on a compact printhead substrate. Each ink drop generator is a thin-film structure formed in printhead substrate that is fluidically coupled to an ink supply device and includes a nozzle. Ink is supplied to the ink drop generators and at the appropriate time heated and ejected from the associated nozzle.
In a preferred embodiment, the ink drop generator density on the compact printhead exceeds 10 ink drop generators per square millimeter and the compact printhead contains at least 350 nozzles. The ink drop generators (and corresponding nozzles) are arranged in at least three parallel rows. Each row is staggered (or offset) relative to an adjacent row to provide a greater effective pitch that a non-staggered arrangement.
The present invention also reduces costs associated with a printhead having a high-density of ink drop generators by placing the generators on a compact printhead. In order to facilitate a high density of ink drop generators on a compact substrate the present invention includes several techniques to improve thermal efficiency. One technique for improving thermal efficiency is providing thermally-efficient ink drop generators having a thin-film structure that includes high-resistance resistors and a thin passivation layer.
The high-density arrangement of ink drop generators on a compact printhead provides high-performance printing in a portable and low-cost package. Specifically, by using thermally-efficient ink drop generators and providing exceptional thermal control of the compact printhead, the present invention can provide high-speed, high-resolution and high-quality printing. The present invention also includes a method of high-performance printing using the compact ink jet printhead of the present invention.
Other aspects and advantages of the present invention as well as a more complete understanding thereof will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. Moreover, it is intended that the scope of the invention be limited by the claims and not by the preceding summary or the following detailed description.